The principal aims of the proposed research are (1) the development of novel spectrofluorimetric methods for the elucidation of the structure and dynamics of macromolecular assemblies; and (2) the application of these techniques to obtain insight into the function of selected excitable membrane systems. We propose to continue several lines of research that have been fruitful: (1) the use of energy transfer as a spectroscopic ruler to measure distances in 10 to 80 angstrom range; (2) the use of nanosecond fluorescence polarization spectroscopy to characterize rapid rotational motions; (3) the design, synthesis and evaluation of specific, sensitive fluorescent labels; and (4) the determination of the conformational correlates of ion transport in spherical bilayer membranes. The time now appears ripe for applying these techniques to eludicate facets of the architecture and dynamics of cell surfaces. We plan to carry out the following studies in this regard. Our nanosecond fluorescence apparatus and a fluorescence correlation spectrometer will be interfaced with a fluorescence microscope. Nanosecond fluorescence microscopy will provide information about energy transfer and hence about proximity relationships on cell surfaces. Fluorescence correlation spectroscopy should reveal translational motions and conformational transitions that occur in the time range from about 10 to minus the 5th power sec to several seconds. These studies will be carried out on neuroblastoma cells and on normal neurons in tissue culture.